This invention is directed to a method of polymerization and/or copolymerization of diolefins selected from the group of monomers consisting of trans-1,3-pentadiene and isoprene. It is also directed to catalyst systems used in these polymerizations. The products of these polymerizations have properties ranging from rubbers to plastics and thereby find utility in the preparation of vulcanized rubber products and plastics. The polymers which have glass transition temperatures (Tg's) which are relatively low may be utilized in tire carcass stocks while those with high Tg's may be used in tread stocks.
More specifically, this invention is directed to the use of a tertiary catalyst system comprising (A) an organometallic compound selected from the group consisting of trialkylaluminums, dialkylaluminum hydrides, dialkylmagnesiums, and dialkylzincs, (B) a soluble chromium compound selected from the group consisting of chromium salts of organic acids containing from 2 to 20 carbon atoms, organic complex compounds of chromium containing tridentate organic ligands, and .pi.-bonded organochromium compounds, and (C) a member selected from tris(2-chloroethyl)phosphite, dialkyl hydrogen phosphites and diaryl hydrogen phosphites, to polymerize and copolymerize diolefins selected from the group of trans-1,3-pentadiene and isoprene.
Belgian Patent Nos. 530,617 and 535,082 and U.S. Pat. No. 2,825,721 were among the first to describe a partially reduced or partially oxidized chromium oxide supported on silica alumina cracking catalyst for the polymerization of ethylene.
U.S. Pat. No. 3,114,743 reported that butadiene was polymerized to a trans-1,4-polybutadiene using either CrCl.sub.3 and diethylaluminum hydride or chromium acetylacetonate and triethylaluminum; the same catalyst polymerized isoprene but the polymer was not described. However, Belgian Patent No. 543,292 indicates that when diisobutylaluminum hydride-CrCl.sub.3 were used to polymerize isoprene, a 1,4-polyisoprene was obtained.
Italian Patent No. 538,453 and British Patent No. 835,752 indicate that a binary catalyst system of chromium acetylacetonate and triethylaluminum polymerizes butadiene to a prevailingly 1,2-enchained linear polybutadiene and isoprene to prevailingly 3,4-polyisoprene.
Polyisoprenes prepared with a binary catalyst system such as chromium acetylacetonate plus triethylaluminum or tris(.pi.-allyl)chromium plus a Lewis acid were generally low molecular weight liquids which had intrinsic viscosities of about 0.2 dl/g. This is reported in J. Polym. Sci., Chem. Ed 11, 2489 (1973).
In Proc. Acad. Sci. USSR 169, 790 (1966) it is reported that the presence of oxygen with tris(crotyl)chromium during the polymerization of butadiene caused almost complete inversion of the polymer microstructure from normally about 83 percent 1,2- to about 95 percent trans-1,4-polybutadiene. It has been reported in Bull. Acad. Sci. USSR, Div. Chem. Sci., 2059 (1967) that trichloroacetic acid with tris(crotyl)chromium polymerized butadiene to 93 percent cis-1,4-polybutadiene.
Polymers having high 1,4-trans-enchainments of isoprene and butadiene have been prepared using a chromia supported on silica-alumina, as reported in Dokl. Akad. Nauk. USSR 124, 595 (1959) and Polym. Sci. USSR 9, 1802 (1968).
Chem. Abs. 80, 109590 v (1974) reports the preparation of 1,2-polybutadiene by polymerizing butadiene in the presence of hydrogen using chromium acetylacetonate, dibutylphosphonate and triisobutylaluminum.
Chem. Abs. 80, 4644 n. (1974) reports that a polymer analyzing 95 percent 1,2-polybutadiene was prepared using a chromium compound, an organoaluminum compound and phosphoric acid ester catalyst system.
It has been reported in Kobunshi Ronbunshu 31, 754 (1974) that a binary catalyst system comprised of chromocene (dibenzene chromium) and an organic halide polymerized butadiene to a polymer having a microstructure very similar to that produced by radical initiators, that is, about 67% trans-1,4; 15% cis-1,4- and 18% 1,2-polybutadiene.
In U.S. Pat. Nos. 3,429,940 and 3,804,913 there is reported that a ternary catalyst system comprising chromium acetylacetonate, triethylaluminum and an aliphatic halide, such as t-butyl chloride, oligomerized conjugated diolefins such as butadiene, isoprene and piperylene, to large ring cyclic trimers such as trimethyl cyclododecatriene.
There is reported in U.S. Pat. No. 3,754,048 that another ternary catalyst system using chromium acetylacetonate, triethylaluminum and a nitrogen containing compound, such as .alpha.-(2-pyridyl)benzylidine-p-toluidine produced oligomers of butadiene, isoprene or piperylene. It is reported therein that the polybutadienes having molecular weights between about 300 and about 1400 were prepared and recovered in about 90 percent yield; less than 10 percent of the polybutadiene had a molecular weight between 1400 and 5500.
Therefore, to summarize, there has been no catalyst system containing chromium which has been previously used to prepare solid elastomers of trans-1,3-pentadiene and isoprene.